1. Field of the Invention
This invention relates to an improved apparatus for detecting the presence of an analyte in a fluid. In particular, phase sensitive differential polarimetry is used to detect a change in optical rotation caused by an enzyme specific reaction.
2. Description of the Prior or Contemporary Art
It is known in the art that certain enzymes can change the optical rotation of a particular substrate. For instance, when sucrose is heated with the enzyme invertase, it is "inverted" to form one molecule of fructose and one of glucose. Since glucose has a specific rotation of +66.5.degree., fructose has a specific rotation of -93.degree., and glucose -52.5.degree., the total rotation changes from +66.5.degree. to (-93+52.5)/2=-20.2.degree. upon inversion. By measuring the change in rotation it is possible to determine the presence of an analyte (such as sucrose).
However, the prior art techniques used to measure optical rotation are not adequate for automatic industrial sampling. As described in "Instrumental Methods of Analysis" by Hobart H. Willard et al, 4th ed. (1965) D. Van Nostrand Company, Inc., at pg. 418, the following cumbersome prior art technique is taught: (1) a solution of sucrose (or other analyte) is poured into a test cell; (2) a polarimeter manually operated by the chemist is used to measure the optical rotation of the sample; (3) an enzyme specific to the analyte (i.e., enzyme invertase) is added to the test cell and it is heated; and (4) the test cell is placed in the polarimeter and the change in optical rotation is manually measured. This prior art technique is not suited for on-line automatic analysis of analyte concentration in an industrial process.